Render blank plot using plot_geo() in ShinyApp R - r

Question

I am doing my final project for data visualization.
I would like to render a map with markers on it using Plotly in ShinyApp. The function I am using is plot_geo(). However, the plot works perfectly in the normal R environment, but it fails to render in ShinyApp, only displaying the blank plot. And also no error message is reported.
I have been stuck here for long. Can anyone help? Thanks!
My code (ShinyApp)
library(shiny)
library(plotly)
library(RColorBrewer)
library(ggplot2)
# Define UI for application
ui <- fluidPage(
# Application title
titlePanel("Times University Ranking"),
# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
selectInput("year",
"Select a year",
c(2011:2016))
),
# Show a plot of the generated distribution
mainPanel(
plotOutput("map")
)
)
)
# Define server logic required to draw a histogram
server <- function(input, output) {
times <- data.frame(read.csv("./times.csv", header = TRUE))
d <- reactive({
a <- subset(times, year == input$year)
return (a)
})
g <- list(
scope = 'world',
projection = list(type = 'Mercator'),
showframe = FALSE,
showland = TRUE,
showsubunits = TRUE,
landcolor = toRGB("gray95"),
subunitcolor = toRGB("gray85"),
countrycolor = toRGB("gray65"),
countrywidth = 0.5,
subunitwidth = 0.5
)
output$map <- renderPlotly({
p <- plot_geo(data = d(), lat = ~lat, lon = ~lon,
color = ~as.numeric(rescale),
mode = 'markers', colors = "Spectral") %>%
add_markers(text = ~paste(paste("Rank:", world_rank),
university_name, country,
year, sep = "<br />"),
hoverinfo = "text") %>%
colorbar(title = "World Rank") %>%
layout(title = paste(input$year, "Times University Ranking on the Map"),
geo = g)
})
}
# Run the application
shinyApp(ui = ui, server = server)
Normal R code
library(plotly)
library(RColorBrewer)
input <- read.csv("times.csv", header = TRUE)
df <- data.frame(subset(input, year == 2015))
df <- df[sort.int(df$No, decreasing = TRUE), ]
# geo styling
g <- list(
scope = 'world',
projection = list(type = 'Mercator'),
showframe = FALSE,
showland = TRUE,
showsubunits = TRUE,
landcolor = toRGB("gray95"),
subunitcolor = toRGB("gray85"),
countrycolor = toRGB("gray65"),
countrywidth = 0.5,
subunitwidth = 0.5
)
p <- plot_geo(data = df, lat = ~lat,
lon = ~lon, color = ~as.numeric(rescale), mode = 'markers',
colors = "Spectral") %>%
add_markers(
text = ~paste(paste("Rank:", world_rank), university_name,
country, year, sep = "<br />"),
hoverinfo = "text") %>%
colorbar(title = "World Rank") %>%
layout(title = '2016 Times University Rankings on the map', geo = g)